The Monkey Cage highlights an experiment done by researchers at Arizona State University in 2004. They had three seperate groups of people watch a debate between George. W. Bush and John Kerry. One group only watched the debate. Another group watched the debate plus 20-minutes of post-debate coverage from NBC. The third group watched the debate, then read 20 minutes of post-debate analysis on CNN.com.
The people who watched just the debate or read coverage on their own thought John Kerry won the debate. Those who watched NBC thought the opposite.
Our findings suggest that voters' attitudes are influenced by the arguments presented directly by the candidates during the debate as well as by the media's instant analyses of the candidates' debate performances….the impact of the candidates' messages was often altered by the media's instant analyses.